Isotactic polpropylene brush bristle and brush containing such bristles



Dec. 3, 1963 P. c. MUNT 3, ISOTACTIC POLYPROPYLENE BRUSH BRISTLE ANDBRUSH CONTAINING sucn BRISTLES 2 Sheets-Sheet 1 Original Filed March 20,1959 INVENIOR ATTORNEYS Dec. 3, 1963 P. c. MUNT 3,112,508

ISOTACTIC POLYPROPYLENE BRUSH BRISTLE AND BRUSH CONTAINING SUCH BRISTLESOriginal Filed March 20, 1959 2 Sheets-Sheet 2 FIG.4

IHIITI INVENTOR. PLUMMER C. MUNT BY @M W ATTORNEYS United States Patent3,112,503 ESGTACTHQ PULYPRQPYLENE BRUSH BEETLE AND BRUfil-l CGNTAENENGSUQH BRlSTLES Plummet C. Murat, Burlington, Vt, assignor to E. B. 8: A.C. Whiting onipany Original application Mar. 20, B50, Ser. No. $00,840,new Patent No. 3,059,991, (3st. 23, 1961. Divided and this applicationul y 26, 1962, er. N 212,639

2 (Ilaims. (El. 15-15%) This invention relates to oriented bristles ofisotactic polypropylene.

In compliance with Title 35, Uni ed States Code, section 120, specificreference is hereby made to application Serial No. 800,840, filed March20, 1959, now US. Patent No. 3,059,991 of which the present applicationis a division.

Melt extruded, stretch oriented fibers of isotactic polypropylene havebeen reported, for instance, in an article by V. Erlich appearing inModern Textiles Magazine, November 1958, pages 59-66. Such fibers havehigh tensile strength and other desirable properties. However, thefibers or filaments of oriented isotactic polypropylene producedheretofore had a marked tendency to curl and are, therefore, unsuitablein many applications especially as synthetic bristles. Other objectionsto the prior art fibers are lack of stiffness, air bubbles entrainedwithin the fibers and nubs of irregularity of cross-section along thelength of the fibers.

It has been discovered that straight, highly stiff and uniform orientedfilaments may be manufactured from crystalline isotactic polypropylenehaving a high molecular weight as indicated by a melt index of from 28grams/ten minutes to 30 grams/ ten minutes under a load of kilograms at250 C., which melt index is determined in accordance with ASTM D1238-52T employing the load and temperature specified. In order to obtainthese desirable filaments, a process comprising certain specific stepsalso must be followed. In outline, the steps of the process are meltextruding filaments of the polypropylene, quenching the freshly extrudedfilaments in a liquid non-solvent bath for the filaments maintained at atemperature of from about 40 F. to about 60 F., gradually heating thequenched filaments to their softening temperature, i.e. from about 260F. to about 305 F., stretching the heat softened filaments from aboutsix to about eleven times their length, and quenching the filaments asecond time after stretching in a liquid nonsolvent bath for thefilaments maintained at a temperature of at least as low as about 60 F.

It is therefore the principal object of this invention to provide anovel synthetic bristle of polypropylene. Other objects and advantagesof the invention are apparent from the complete description thereofwhich follows.

The aspects of this invention that are capable of illustration are shownin the accompanying drawings.

FIGURE 1 is a schematic view of a suitable overall arrangement ofapparatus for carrying out the method of this invention.

FIGURE 2 is an enlarged view of the extrusion head in FIGURE 1.

FIGURE 3 is a magnification of the cut end of a bristle made inaccordance with this invention.

FIGURE 4 is an elevational view of a brush.

The drawings are further explained in detail as follows:

In FIGURE 1, a hopper 5 contains the starting material 6, pelletizedcrystalline isotactic polypropylene. The polypropylene pellets 6 arepre-heated in the hopper 5 to about 180 F. From the hopper 5, thepolypropylene 6 is conveyed by a heated screw mechanism 7 or through3-,l i258 Fatentecl Dec. 3, 1963 any conventional thermoplasticextruder, to a heated extrusion head 8. Thus, the temperature of thepolypropylene is raised above its melting point as it is conveyed to theextrusion head 8 and extruded through orifices 30 shown in FIGURE 2, asone or more filaments 10. A preferred extrusion temperature for thepolypropylene is about 480 F. when the filaments 10 are exruded at alinear rate of from about 18 to about 30 feet per minute from theorifices 30 which range from about 8 mils to about 500 mils in diameter.The term mils as used herein denotes a linear measurement of onethousandth of an inch. The extruded filaments 10 are guided into thequench bath 12, containing a liquid non-solvent for isotacticpolypropylene, e.g., water, by a guide roll 11. The bath 12 ismaintained in a suitable tank 13 at a emperature of at least as low asabout 60 F., the lower temperature limit for bath 12 being determined bythe brittleness of unoriented isotactic polypropylene at lowtemperatures as Well as practical cost considerations. Thus, a practicallower temperature limit for bath 12 is about 40 F. Above the given uppertemperature limit for bath l2, later processing difficulties such as theformation of nubs in filaments 10 may occur. The term nub describes acondition in the filaments wherein, at spaced intervals, the filament isenlarged. The preferred operating temperature for bath 12 is about 55 F.An immersion time of from about 8 seconds to about 20 seconds of thefilaments 10 in the quench bath 12 is required to produce straight ornub-free, filaments. Accordingly, the path of travel in bath 12 isvaried in length as the linear rate of extrusion is varied, and Viceverse, to provide adequate immersion time in the bath 12 in theforegoing range.

The extruded filaments 10 are transported around a stationary pin 14 inthe quench bath l2 and out of the bath 12 thence over roll 15 and into ahot air conditioning oven 18. Continuing over driven rolls 16 as shown,the filaments 10 follow a zig-zag path in the oven 18 as heated air iscirculated from overhead as indicated by arrows 19. Each succeedingdriven roll 16 over which a filament 10 passes is driven at a slightlyincreased peripheral speed from that of the preceding roll by anysuitable means. This slight increase in peripheral speed providessufiicient tension on the filaments 10 to prevent sagging as they passthrough the oven 18 and may impart some stretch on the filaments 10 of atotal of about 25% over six or more driven rolls. It is not essential,however, to impart any stretch in the filaments as they pass over therolls 16 and only sufiicient tension therein to prevent sag isnecessary. The primary purpose of the driven rolls 16, or a similarsystem, is to provide a heat exchange relationship between the filamentsl0 and heated air or other fluid medium in the oven whereby thefilaments are uniformly softened by heat. The crystalline isotacticpolyproylene employed for the purposes of this invention has a softeningtemperature in the range of from about 260 F. to about 305 F. orslightly higher, but below the crystalline melting point of the polymer.If the temperature employed in the oven is below the lower given limitfor the softening temperature, stretching without nub formation in thefilaments is difiicult to achieve. It has been found that if the oven ismaintained at a temperature near the given upper limit of the softeningtemperature of the polymer, i.e. from about 300 F. to about 305 F., asuperior end product results in which the filaments so conditioned andproduced, exhibit little or no fibrillation characteristics. It issometimes desired, however, that the filaments 10 exhibit fibrillationcharacteristics particularly for use as bristles, in which case, thetemperature in the oven 18 should be maintained at from about 260 F. toabout 280 F. The filaments 10 become heat softened after being subjectedto hot gas in Z the oven 18 for about from 1 to 2 minutes and attain thesame temperature as the air entering the oven 13.

The filaments ll) after leaving the last and uppermost driven roll 16,are snubbed with a three roll assembly 17, each roll of which is drivenat about the same as or a higher peripheral speed than that of the lastdriven roll 16. A fast roll 24) is provided just outside the oven 1%,and, between the assembly 17 and the fast roll 2%, the filaments it? arestretched from about 6 to about ll times or more of their length. Theperipheral speed of fast roll 20 is about 6 to about 11 times that ofthe assembly rolls l7. Filaments which are suitable as bristles when cutor staplized into various lengths are produced by employing a stretch ofabout 6 and a half times the original length, i.e., a stretch ratio ofabout 6.5 to 1, is sufficient and preferred. For continuous cordagefilaments of from 500 to 600 denier, a stretch ratio of at least 10 or11 to l is preferred to produce filaments with tensile strengths inexcess of 6 grams/ denier and a dry or wet elongation at breaking of 15%or less.

A high degree of molecular orientation is effected in hot melt extrudedisotactic polyproylene filaments which are heat stretched in accordancewith this invention as is evidenced by characteristic X-ray diffractionpatterns of such filaments. The oriented filaments iii are then guidedaround a dip roll 21 in a second quench bath 22 contained in a tank 23.The requirements for this second quenching are essentially the same asthose employed in quenching the freshly extruded filaments, i.e, justafter filament extrusion. However, it is possible to use lower quenchingtemperatures in this second quenching step because isotacticpolypropylene filaments oriented in accordance with this invention arenot brittle at temperatures as low as 65 F. Thus, the second quenchingsuitably is carried out by immersing the stretch oriented filaments in aliquid non-solvent bath for the filaments at a temperature of at leastas low as about 60 F, preferably from about 35 F. to 55 F. The optimumtemperature for the second quench bath 22 is about 55 F. The duration ofthe immersion in the second quenching bath is, preferably, from aboutone to about 12 seconds depending upon the cross-sectional diameter ofthe oriented filament which is approximately as many times less as thesame diameter of the extruded filament prior to stretching, as thesquare root of the stretch ratio.

The oriented filaments it are drawn from the bath 22 by a drivensnubbing system such as a pair of snubbing rolls 24 and collected on areel 25 supported on a frame 26. The snubbing rolls 24 cooperate withthe snubbing assembly 17 to control stretching between the assembly 17and the fast roll 20.

Referring to FIGURE 2, there is shown an enlarged view of the extrusionhead 8, the general reference numeral in FIGURE 1, showing the orificesin an orifice bar 31 held to a hollow body 32 by the bolted clamps 33,the hollow body 32 being suspended in the bracket members 34. Theelectrical resistance heating elements 35 supply heat to the extrusionhead. The orifices fill may be of any cross-sectional shape, but for theproduction of bristles the preferably round. The orifices 39 may becountersunk on the side of bar 31 which is inside the body 32, orconically tapered so that the orifices 3h become smaller in diametertoward the point of extrusion. Such countersinking or tapering of theorifices 3b is done to reduce the resistance to the flow of moltenpolypropylene therethrough. The structure in FIGURE 2 is typical of Whatmay be employed to extrude the filaments or bristles of this invention.

It is apparent from the above description of the method of thisinvention that the essential features thereof are melt extrudingfilaments and other shaped articles of crystalline isotacticpolypropylene, first quenching the freshly extruded filaments and thenquenching the filaments at second time after they have been stretched ina heat softened condition as descrlbed. Both quenching 4 stepspreferably are carried out by immersing the filaments in a bath of aliquid non-solvent for the filaments. The first such quench bath ismaintained at a temperature of from about 40 F. to about 60 F., and thesecond bath ismaintained at a temperature of at least as low as about 60F.

A magnified view (300x) of an end of a bristle made by applying ashearing force transversely of the longitudinal axis of an orientedfilament 10 produced in accordance with this invention is shown inFTGURE 3. The shearing force must be sufficient to sever the filamentand is applied preferably, along a line or path perpendicular to alongitudinal axis of the filament. The shearing force is preferablyapplied to a bundle or two containing at least two or three hundredfilaments. The sheared-off end 36 is rounded and has a pointed lip orbarb 37 extending laterally, substantially perpendicularly to thelongitudinal axis of the oriented filament ll This rounded end isextremely resistant to abrasion. Consequently, bristles so cut from thefilaments of this invention are useful in brushes particularly forstreet, cleaning, removal of rust from metal as well as in other typesof brushes designed to provide a harsh abrasive property.

The bristles, prepared according to this invention also have uniquereturn characteristics as compared with other synthetic bristles whenarcuatcly flexed or bent and then released at one point along the arcwhile being held at another point. The bristle, or a given length of afilament returns, upon release, .to substantially its original straightunfiexed position as will nylon bristles, but the rate of return isconsiderably slower than that of a conventional or'ented 66 nylonbristle having the same dimensions. This property is especiallyimportant in broom, dust brush and paint brush bristles. Thus, thisproperty of these bristles prevents flicking of dirt or paint when thebrush is used in its intended environment. These bristles, moreover,provide a brush in which the bristles do not become permanently set in acurled position after a short time in use. Filaments of this inventionfrom about 5 mils to about 29% mils in mean diameter and cut intobristles varying in length from about A; of an inch to 15 inches or morehave the return characteristic described. Pilaments made in accordancewith this invention of from about 5 mils to about mils in mean diameterare preferred for making bristles.

FIGURE 4 illustrates a conventional brush 4t) which comprises a handleil containing abrasion resistant brush bristles d2 of oriented meltextruded isotactic polypropylene which has been immediately quenchedafter extrusion in a bath of a non-solvent liquid for said polymer at'atemperature of at least as low as about 60 F.

In the broad sense, the process of this invention may be applied toextruded shaped articles other than filaments. In particular, shapedarticles may be produced by the process that have at least one dimensionwhich is relatively large with respect to at least one other dimension,for example, melt extruded ribbons and films. Such articles may be heatstretched along more than one of their large dimensions, i.e., laterallywith respect to the direc tion of extrusion in addition tolongitudinally. Thus, this invention may be employed to prepare verythin exceptionally tough tapes which have a variety of uses, includingthat of a flexible base for electrically responsive coatings used in therecording field.

The starting material for this invention is a high molecular weight,solid, crystalline, substantially isotactic polymer of propylene havinga crystalline melting point as determined by birefringence, of at leastabout 329 1 preferably about 333 F. and a specific gravity of about 0.90to 0.91. A preferred isotactic polypropylene for the purpose of thisinvention has a melt index of from about 28 grams/ ten minutes to about30 grams/ten minutes under a load of 10 kilograms at a temperature of250 C., the melt index being determined substantially in accordance withASTM 131238-521" employing the load and temperature herein specified andmeasuring the weight of polymer extruded by the ASTM procedure over aperiod of ten minutes. Solid, high molecular weight isotacticpolypropylene may be prepared in accordance with procedures taught by G.Natta in the Journal of Polymer Science, vol. XVI, pp. 143-154 (1955). Amore recent review on methods of making the polymer is in an article byG. Bier in Kunstsoffe, Bd. 48, pp. 354-362 (August 1958). The disclosureof these two articles are hereby incorporated by reference into and madea part of this disclosure.

The following working examples illustrate the invention and constitutethe best mode contemplated of carrying out the invention representingpreferred embodiments thereof.

Example 1 Pellets of crystalline isotactic polypropylene having acrystalline melting point of 333 F, specific gravity of 0.90 and a meltindex of 28 grams/ten minutes under a kilogram load at a temperature of250 C., were preheated in a hopper to 130 F. feeding a 2" Hartigextruder. The temperature of screw barrel at the feed end was 400 F. andincreased to 480 F. at the outlet end which was connected to a heatedextrusion head fitted with an 11 inch extrusion bar having 15 verticallydisposed orifices 78.5 mils in diameter. The temperature across theouter head wall opposite the connection to the Hartig extruder, wasobserved to be 470 -F. although the melted polymer therein was probablyat a temperature near 480 F. The Hartlg extruder was operated to extrudefilaments uniformly from the orifices at a linear rate of 19 ft./minute. The so extruded filaments were guided into an aqueous quenchbath at a temperature of 55 F. The length of travel for each filamentbetween the point of extrusion and the surface quench bath was twoinches and that in the quench bath 64 inches. From-the quench bath, thefilaments were directed into the bottom of an oven in which hot air wascirculated from top to bottom at a rate of 3100 cubic feet/minute sothat the oven had air temperatures of 260 F., 280 F. and 300 F. in thelower, middle and upper regions respectively thereof. In the oven, thefilaments followed a zig-zag path over a series of rolls driven atgradually increasing peripheral speeds to prevent sagging of thefilaments and thereby impart tension such that a 25% increase infilament length occurred. The filaments traveled generally upward aswell as back and forth as shown in FIGURE 1 of the accompanying drawingfor a time interval of 1 /2 minutes. At the top or" the oven, thefilaments passed through a three-roll snubbing system to preventstretching prior to that point and control stretching between thesnubbing rolls and a fast roll just outside the oven. The filaments werestretched six and one-half times their length to give oriented filaments30 mils in diameter. After stretching, the oriented filaments werequenched a second time by immersion in an aqueous bath at 55 F. for twoseconds, drawn between two snubbing rolls driven at the same peripheralspeed as the fast roll, and collected on a reel. X-ray diffraction bythe filaments gave characteristic sharp pattern lines indicating a highdegree of orientation of the polymer crystallite structure.

.oxample 2 A bundle of 150 of the filaments made in Example 1 were cutinto bristles 2 /2 inches in length by a guillotine type cutter.Microscopic examination (300x) of the cut ends of these bristlesrevealedthat each bristle had a rounded end with a pointed lip or barbextending perpendicularly to a longitudinal axis of the bristle as shownin FIGURE 3. Several bristles selected at random were flexed or bent ina 180 are by grasping the bristles near each end and bending. One endwas then released and each bristle made a substantially complete returnto its original straight alignment after spring-like oscillations nearcomplete return. Comparisons with oriented 66 nylon bristles of the samesize demonstrated that the bristles of this invention had slower returnthan nylon bristles under the same flexing conditions, but were notpermanently set or distorted by such flexing.

Example 3 A number of the bristles in Example 2 were assembled and setas bristles in a general utility hand brush. This brush was successfullyused to remove scale from a piece of badly rusted steel. The same brushalso was employed along with a strong detergent solution in scrubbing aceramic tile floor.

Example 4 Filaments were made of the same batch of isotacticpolypropylene and in the same manner as in Example 1 except that the airtemperature of the top of the oven and that of the filaments whenstretched was 280 F. Filaments resulted which exhibited fibrillationespecially when broken under tension while the filaments of Example 1when similarly broken did not fibrillate. The tensile strengths of thefilaments of this example and those of Example 1 were both in excess of100,000 pounds per square inch.

' Example 5 Example 1 was repeated except that an extrusion bar with 30orifices 24 mils in diameter was used. Filaments 6 mils in diameter wereproduced. Two inch bristles cut from the filaments had complete returncharacteristics when arcuately flexed and released.

Example 6 Example 1 again was repeated with the 30 orifices, 24 milorifice diameter extrusion bar. The filaments were stretched 10 to 1 at305 F. and otherwise processed as set forth in Example 1. The filamentsso prepared were 560 denier and had a tensile strength of 6.87 grams/denier with a dry elongation at breaking of 12.2%. In view of theseproperties, the filaments made outstanding stranded cordage of from /8to /2 inch in diameter.

Example 7 Crystalline isotactic polypropylene having a crystallinemelting point of 333 F., a specific gravity of 0.90 and a melt index of28 grams/ 10 minutes under a load of 10 kilograms at a temperature of250 (3., was extruded through a thin slot, A inch x 1 /2 inches, at 280F. This ribbon-like extrusion was quenched in an aqueous bath at 45 F.and stretched two and a half times its length at a temperature of 280 F.A strong, tough webbing material having a thickness of about 40 mils wasthereby made. It was found to be useful for handing wooden cratescontaining heavy articles such as refrigerators.

It is to be understood that the foregoing description and examples areillustrative only and do not limit the spirit and scope of my inventionas defined in the appended claims.

Comparison Example Filaments were made of the same batch of isotacticpolypropylene as used in Example 1 and under the same conditions exceptthat both the quench bath after extrusion and the second quench bathwhich follows stretching, were maintained at a temperature of X-raydiffraction of these filaments gave the same patterns as, but lessdefined than those of the filaments of Example 1, indicating a lowerdegree of orientation of the polymer crystal ite structure.

I claim:

1. An abrasion resistant brush bristle of draw-oriented, melt extruded,liquid quenched at a temperature of about 40 F. to about 60 F.,isotactic polypropylene having a tensile strength of about 6grams/denier, a specific gravity of from about 0.90 to 0.91, saidbristle having been stretched from about 6 to 11 times its originallength.

2. A brush containing abrasion resistant brush bristles ofdraw-eriented, melt extruded, liquid quenched at a temperature of about40 F. to about 60 F., isotaetic peiypropylene having a tensile strength01' about 6 grams/ denier, a specific gravity of from about 0.90 to0.91, said bristles having been stretched from about 6 to 11 times theiroriginal length.

References Qited in the file of this patent laughter Dec. 23, Reis May23, Peterson June 13, Terry et a1. May 22, Kutik June 4, Reis et a1 Feb.2, Maragliano et a1. Aug. 2, Shaw Feb. 20, Heumarm Sept. 18,

FOREIGN PATENTS Switzerland Dec. 15, France Nov. 22,

1. AN ABRASION RESISTANT BRUSH BRISTLE OF DRAW-ORIENTED, MELT EXTRUDED,LIQUID QUENCHED AT A TEMPERATURE OF ABOUT 40*F. TO ABOUT 60*F.,ISOTACTIC POLYPROPYLENE HAVING